Circuit-switched services over SAE/LTE networks

ABSTRACT

A method and apparatus for providing both Mobile Terminated, MT, and Mobile Originated, MO, circuit switched (CS) services such as Short Message Service, SMS, services in networks utilizing CS Fallback and CSoLTE-I architectures. An extended SGs interface referred to as SGs+ is implemented between a Mobility Management Entity, MME, in an SAE core network and a Mobile Switching Center Server, MSC-S. The SGs+ interface supports transmission of upper layer CS packet data units while utilizing either connectionless or connection-oriented Signaling Connection Control Part, SCCP, operation. The non access stratum, NAS, signaling support between the User Equipment, UE, and the MME is extended to provide support for both MT SMS and MO SMS service.

This application claims the benefit of U.S. Provisional Application No.60/984,426, filed Nov. 1, 2007, the disclosure of which is fullyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to wireless telecommunication networks.More specifically, and without limitation, the invention is directed toa system and method for providing circuit-switched (CS) services overSAE/LTE networks, and in particular for supporting the Short MessageService (SMS) in the CS Fallback and CSoLTE-Integrated networks.

BACKGROUND

The following abbreviations are utilized throughout this document:

3GPP Third Generation Partnership Project

AS Application Server

CM Connection Management

CSoLTE CS Services over LTE Radio Access

CS Circuit-Switched

DTM Dual Transfer Mode

eMSC-S evolved MSC Server

EPC Evolved Packet Core

EPS Evolved Packet System

E-UTRAN Evolved UTRAN

FDMA Frequency Division Multiple Access

GSM Global System for Mobile Communications

IASA Inter-Access Anchor

IMS IP Multimedia Subsystem

LAI Location Area Identifier

LTE Long Term Evolution

MME Mobility Management Entity

MSS Mobile Softswitch Solution

NAS Non Access Stratum

OFDM Orthogonal Frequency Division Multiplexing

PCRF Policy Charging Rule Function

PMSC Packet MSC

PCSC Packet CS Controller

PS Packet-Switched

RRC Radio Resource Control

SAE System Architecture Evolution

SAI Service Area Identifier

SCCP Signaling Connection Control Part

SC-FDMA Single Carrier Frequency Division Multiple Access

TA Tracking Area

UPE User Plane Entity

UTRAN Universal Terrestrial Radio Access Network

WCDMA Wideband Code Division Multiple Access

Mobile CS services based on GSM and WCDMA radio access are a world-widesuccess story and provide telecommunication services with a singlesubscription in almost all countries of the world. The number of CSsubscribers is still growing rapidly, boosted by the rollout of mobileCS services in dense population countries such as India and China. Thissuccess story is furthermore extended by the evolution of the classicalMSC architecture into a softswitch solution, which utilizes a packettransport infrastructure for mobile CS services.

Recently, the 3GPP work item “Evolved UTRA and UTRAN” (i.e., E-UTRAN,started in summer 2006) defined a Long-Term Evolution (LTE) concept thatassures competitiveness of 3GPP-based access technology. It was precededby an extensive evaluation phase of possible features and techniques inthe RAN workgroups that concluded that the agreed system concepts canmeet most of the requirements and no significant issue was identified interms of feasibility.

LTE utilizes OFDM radio technology in the downlink and SC-FDMA for theuplink, allowing at least 100 Mbps peak data rate for downlink data rateand 50 Mbps for uplink data rate. LTE radio can operate in differentfrequency bands and is therefore very flexible for deployment indifferent regions of the world.

FIG. 1 is a simplified block diagram of nodes in a System ArchitectureEvolution (SAE) Core Network (SAE CN) 11 and an LTE Radio Access Network(LTE RAN) 12. In parallel to the LTE RAN (E-UTRAN) standardization, 3GPPalso drives an SAE work item to develop an evolved core network alsocalled the Evolved Packet Core (EPC). The E-UTRAN and EPC together buildup the Evolved Packet System (EPS). The SAE CN 11 is made up of corenodes, which may be further split into a Control Plane (MobilityManagement Entity, MME) node 13 and a User Plane (SAE Gateway, SAE-GW)node 14. In the terminology currently used, the SAE-GW contains bothUser Plane Entity (UPE) and Inter-Access Anchor (IASA) functionality.The SAE-GW also has two different roles defined: Serving GW and PacketData Network (PDN) GW. The term SAE-GW is used herein for both theServing GW and the PDN GW. The MME 13 is connected to an eNodeB 15 viaan S1-MME interface 16, and the SAE-GW 14 is connected to the eNodeB viathe S1-U interface 17. The X2-UP and X2-CP interfaces between eNodeBsare not relevant to the present invention. The SAE architecture isfurther described in 3GPP TS 23.401 and 23.402.

Common to both LTE and SAE is that only a Packet Switched (PS) domainwas initially to be specified, i.e., all services are to be supportedvia the PS domain. GSM (via DTM) and WCDMA, however, provide both PS andCS access simultaneously. Thus, if telephony services are to be deployedover LTE radio access, an IMS-based service engine is mandatory. It hasbeen recently investigated how to use LTE/SAE as access technology tothe existing Mobile Softswitch Solution (MSS) infrastructure. This work,referred to as “CS over LTE” (CSoLTE) or the longer name “CS domainservices over evolved PS access,” is documented in 3GPP TR 23.879 and in3GPP TS 23.272.

FIG. 2 is a simplified block diagram of a CSoLTE general architecture20. A Packet MSC (PMSC) 21 serves both traditional 2 G and 3 G RANs 22and the CSoLTE solutions through the LTE RAN 12. The PMSC contains twonew logical functions: a Packet CS Controller (PCSC) 23 and anInterworking Unit (IWU) 24. In addition, there is an SGs interface 25between the MME 13 and an MSC Server (MSC-S) 26. This interface is usedfor Paging and Mobility Management (MM) signaling to attach a mobileterminal 27 in the MSC-S based on, for example, SAE MM proceduresperformed between the terminal and the MME using similar principles asexists already for the Gs-interface between the MSC and SGSN in existingGSM and WCDMA networks and defined in 3GPP TS 29.016 and 29.018. Theprotocol used in the Gs-interface is called BSSAP+ and usesconnectionless SCCP and normal MTP layers (or M3UA with SIGTRAN) in theexisting implementations.

SUMMARY

There does not currently exist a satisfactory system and method forproviding circuit-switched (CS) services over the SAE/LTE networkscurrently being studied in 3GPP, and in particular for supporting theShort Message Service (SMS) in what are referred to as the CS Fallbackand CSoLTE-Integrated networks.

The present invention utilizes an extended SGs interface (a so-calledSGs+ interface) for both Mobile Terminated (MT) and Mobile Originated(MO) SMS services. The prerequisite is that the SGs interface is usedfor Mobility Management (MM) procedures, that is, the UE becomesattached in the MSC-S. Thus, the present invention applies for the CSFallback and CSoLTE-I solutions. In addition, the non access stratum(NAS) signaling support between the UE and the MME is extended toprovide support for both MT SMS and MO SMS service.

In one embodiment, the present invention is directed to a method ofproviding a circuit-switched (CS) service to a User Equipment (UE) overan SAE core network and an LTE radio access network. The method includesextending an SGs interface to provide an SGs+ interface between aMobility Management Entity (MME) in the SAE core network and a MobileSwitching Center Server (MSC-S), wherein the SGs+ interface supportstransmission of upper layer packet data units. The method also includestransferring CS service messages in SGs+ messages sent between the MSC-Sand the MME utilizing the SGs+ interface; and transferring CS servicemessage contents between the MME and the UE via the LTE radio accessnetwork in NAS messages. The method is applicable to both mobileterminated and mobile originated CS services, and different embodimentsaddress UEs in LTE-Idle state and LTE-Active state. In one embodiment,the upper layer packet data units are transmitted utilizingconnectionless Signaling Connection Control Part (SCCP) operation, whilein another embodiment, the upper layer packet data units are transmittedutilizing connection oriented SCCP operation.

In a particular embodiment, the CS service is SMS, and the presentinvention is directed to a method in an MSC-S for delivering an SMSmessage to a terminating UE over an SAE core network and an LTE radioaccess network. The method includes sending a paging request messagefrom the MSC-S to an MME in the SAE core network with an indication thata mobile terminated SMS message is available for the terminating UE;receiving by the MSC-S, a paging response or service request messagefrom the MME; and forwarding the mobile terminated SMS message from theMSC-S to the MME via an extended SGs interface (SGs+) between the MSC-Sand the MME, wherein the SGs+ interface supports transmission of SMSpacket data units. In another embodiment in which the CS service is SMS,the present invention is directed to a method in an MME in an SAE corenetwork for transporting an SMS message from an originating UE over anLTE radio access network and an SAE core network to an MSC-S. The methodincludes receiving in the MME, the mobile originated SMS message fromthe originating UE via an S1 connection; and forwarding the mobileoriginated SMS message from the MME to the MSC-S via an SGs+ interface,wherein an SGs interface is extended to provide the SGs+ interfacebetween the MME in the SAE core network and the MSC-S, wherein the SGs+interface supports transmission of SMS packet data units.

In another embodiment, the present invention is directed to an apparatusin a MME in an SAE core network for providing a CS service to a UEthrough the SAE core network and an LTE radio access network. Theapparatus includes means for utilizing an extended SGs interface (SGs+)with an MSC-S in a CS core network to send and receive SGs+ messages,wherein the SGs+ interface supports transmission of upper layer packetdata units, and the means for utilizing the SGs+ interface includesmeans for transferring CS service messages in SGs+ messages sent overthe SGs+ interface. The apparatus also includes means for transferringCS service message contents between the MME and the UE via the LTE radioaccess network. The apparatus handles both mobile terminated and mobileoriginated CS services, and different embodiments address UEs inLTE-Idle state and LTE-Active state. In one embodiment, the upper layerpacket data units are transmitted utilizing connectionless SCCPoperation, while in another embodiment, the upper layer packet dataunits are transmitted utilizing connection oriented SCCP operation.

In another embodiment, the present invention is directed to an apparatusin an MSC-S for delivering a CS service message to a terminating UEthrough an MME in an SAE core network and an LTE radio access network.The apparatus includes means for sending a paging request message fromthe MSC-S to the MME in the SAE core network with an indication that amobile terminated CS service message is available for the terminatingUE; means for receiving by the MSC-S, a paging response or servicerequest message from the MME; and means for forwarding the mobileterminated CS service message from the MSC-S to the MME via an extendedSGs interface (SGs+) between the MSC-S and the MME, wherein the SGs+interface supports transmission of upper layer packet data units in CSservice messages.

In another embodiment, the present invention is directed to an apparatusin an MME in an SAE core network for delivering a CS service message toa terminating UE through the SAE core network and an LTE radio accessnetwork. The apparatus includes means for receiving from an MSC-S, apaging request message indicating a CS service message is available forthe terminating UE; means for determining whether the terminating UE isin LTE-IDLE state or LTE-ACTIVE state; means for paging the terminatingUE and for returning a paging response or service request message to theMSC-S, upon determining that the terminating UE is in LTE-IDLE state;and means for returning a paging response or service request message tothe MSC-S without paging the terminating UE, upon determining that theterminating UE is in LTE-ACTIVE state. The apparatus also includes meansfor utilizing an extended SGs interface (SGs+) with the MSC-S to sendand receive SGs+ messages, wherein the SGs+ interface supportstransmission of upper layer packet data units. The means for utilizingthe SGs+ interface includes means for receiving an SGs+ downlink datatransfer message sent by the MSC-S in response to the paging responsemessage or service request message, wherein the SGs+ downlink datatransfer message includes the CS service message. The apparatus thenforwards the CS service message content to the terminating UE via theLTE radio access network.

In another embodiment, the present invention is directed to an apparatusin an MME in an SAE core network for forwarding a CS service messagefrom an originating UE over an LTE radio access network and the SAE corenetwork. The apparatus includes means for receiving in the MME, themobile originated CS service message from the originating UE via an S1connection; and means for forwarding the mobile originated CS servicemessage from the MME to the MSC-S via an SGs+ interface, wherein an SGsinterface is extended to provide the SGs+ interface between the MME inthe SAE core network and the MSC-S, wherein the SGs+ interface supportstransmission of upper layer packet data units in CS service messages.

In another embodiment, the present invention is directed to a system forproviding a CS service to a UE through an SAE core network and an LTEradio access network. The system includes an MME in the SAE corenetwork; an MSC-S in a CS core network; and an extended SGs interface(SGs+) for sending and receiving SGs+ messages between the MME and theMSC-S, wherein the SGs+ interface supports transmission of upper layerpacket data units in CS service messages. The MME and the MSC-S includemeans for utilizing the SGs+ interface to transfer CS service messagesin SGs+ messages sent over the SGs+ interface. The system handles bothmobile terminated and mobile originated CS services, and differentembodiments address UEs in LTE-Idle state and LTE-Active state. In oneembodiment, the upper layer packet data units are transmitted utilizingconnectionless SCCP operation, while in another embodiment, the upperlayer packet data units are transmitted utilizing connection orientedSCCP operation. In one particular embodiment, the CS service is theShort Message Service (SMS).

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the essential features of the invention will bedescribed in detail by showing preferred embodiments, with reference tothe attached figures in which:

FIG. 1 is a simplified block diagram of nodes in a System ArchitectureEvolution (SAE) Core Network (SAE CN) and an LTE Radio Access Network(LTE RAN);

FIG. 2 is a simplified block diagram of a CSoLTE general architecture;

FIG. 3 is a simplified block diagram illustrating interfaces utilized bythe PMSC and the PCSC;

FIG. 4 illustrates the Mobility Management (MM) control plane protocolarchitecture between the terminal or UE, eNodeB, MME, and the MSC-S;

FIG. 5 is a simplified block diagram of the entities and functionsincluded in an existing SMS reference architecture;

FIG. 6 is a signaling diagram illustrating the main steps involved inShort Message Mobile Terminated (SM MT) services;

FIG. 7 is a signaling diagram illustrating the main steps involved inShort Message Mobile Originated (SM MO) services;

FIG. 8 illustrates the layers of the SMS protocol;

FIG. 9 is a simplified block diagram illustrating an architecture forproviding SMS over a generic IP access network;

FIG. 10 is a signaling diagram illustrating the actions taken when an MTSMS message is forwarded to the UE in an existing CS Fallback solution;

FIG. 11 is a signaling diagram illustrating the actions taken when an MOSMS message is triggered from the UE in the existing CS Fallbacksolution;

FIG. 12 is a simplified block diagram of an exemplary embodiment of anarchitecture for SMS support in the CSoLTE solutions based on anextended SGs interface (SGs+) according to the teachings of the presentinvention;

FIG. 13A is a signaling diagram illustrating a first embodiment of aprocedure for MT SMS transfer over SGs+ when the terminal is in LTE-IDLEstate;

FIG. 13B is a signaling diagram illustrating a second embodiment of aprocedure for MT SMS transfer over SGs+ when the terminal is in LTE-IDLEstate;

FIG. 14A is a signaling diagram illustrating a first embodiment of aprocedure for MT SMS transfer over SGs+ when the terminal is inLTE-ACTIVE state;

FIG. 14B is a signaling diagram illustrating a second embodiment of aprocedure for MT SMS transfer over SGs+ when the terminal is inLTE-ACTIVE state; and

FIG. 15 is a signaling diagram illustrating an embodiment of a procedurefor MO SMS transfer over SGs+ when the terminal is either in LTE-IDLE orin LTE-ACTIVE state.

DETAILED DESCRIPTION

FIG. 3 is a simplified block diagram illustrating interfaces utilized bythe PMSC 21 and the PCSC 23 in three different embodiments for providingCSoLTE services. The communication between the MS 27 and the PMSC 21 isbased on the Gi interface (now called the SGi interface). This meansthat all direct communication between the MS and the PCSC 23 and the IWU24 in the PMSC is based on IP protocols and that the MS is visible andreachable using an IP-address via the SAE-GW. This communication isdivided into two different interfaces: U8 c for the control plane and U8u for the user plane. The PCSC has also an Rx interface to a PolicyCharging Rule Function (PCRF) 28 for allocation of LTE/SAE bearers.

Three different embodiments for providing CSoLTE service are describedbelow. The first embodiment is called “CS Fallback” and means that theMS or terminal 27 is performing SAE MM procedures towards the MME 13while camping on LTE access. For example, the MME registers the terminalin the MSC-S 26 for CS-based services using the SGs interface 25 shownin FIG. 2. When a page for CS services is received in the MSC-S, thepage is forwarded via the SGs interface to the MME and then to theterminal, which performs fallback to the 2 G or 3 G RANs 22. Thefallback can be based on PS HO, Cell Change order, or terminal-basedselection of the suitable cell in the 2 G or 3 G RAN. Similar behaviorapplies for Mobile Originated (MO) CS services. When these are triggeredand the terminal is camping on LTE access, the terminal falls back tothe 2 G or 3 G RANs and triggers the initiation of the CS service there.

The second embodiment is called CS over LTE Integrated (CSoLTE-I). Inthis embodiment, the same SAE MM procedures as for “CS Fallback” areused over the SGs interface, but instead of performing fallback to the 2G or 3 G RANs, the terminal performs all the CS services over the LTEaccess. This means that the CS services (also called ConnectionManagement (CM) procedures) are transported over IP-based protocolsbetween the PMSC 21 and the terminal 27 over the U8 c and U8 uinterfaces using the LTE access and the SAE nodes such as the SAE-GW 14.

The third embodiment is called CS over LTE Decoupled (CSoLTE-D). In thisembodiment, both MM and CM procedures are transported over IP-basedprotocols directly between the PMSC 21 and the terminal 27 over the U8 cand U8 u interfaces using the LTE access and the SAE user plane nodessuch as the SAE-GW 14.

FIG. 4 illustrates the MM control plane protocol architecture betweenthe terminal or UE 27, eNodeB 15, MME 13, and the MSC-S 26 (e.g., theSGs interface) that is used in the CS Fallback and CSoLTE-I embodiments.FIG. 5 is a simplified block diagram of the entities and functionsincluded in an existing SMS reference architecture 31. The presentinvention provides a system and method for improving the support for SMSin relation to the CS Fallback and CSoLTE-I embodiments.

A Short Message Entity (SME) 32 may send or receive Short Messages. TheSME may be located either in the fixed or mobile networks and isnormally out of scope in the standardization. A Service Center (SC) 33,also referred to as a Short Message Service Center (SMSC) is responsiblefor the relaying, storing, and forwarding of a short message between anSME and an MS 27. An SMS Gateway MSC (SMS-GMSC) 34 is a function of anMSC for receiving a short message from an SC, interrogating a HomeLocation Register (HLR) 35 for routing information and SMS information,and delivering the short message to the MSC-S 26 or the SGSN 36 of therecipient MS. An SMS Interworking MSC (SMS-IWMSC) 37 is a function of anMSC for receiving a short message from within the PLMN (i.e., from theMS either via the MSC-S or the SGSN) and submitting it to the recipientSC. The SC, SMS-GMSC, and SMS-IWMSC may be implemented in the samephysical node.

The Short Message Service comprises two basic services:

-   -   SM MT (Short Message Mobile Terminated); and    -   SM MO (Short Message Mobile Originated).

FIG. 6 is a signaling diagram illustrating the main steps involved in SMMT services. The SMS transfer is performed over a signaling connection.SM MT denotes the capability of the GSM/UMTS system to transfer a shortmessage submitted from the SC 33 to one MS 27, and to provideinformation about the delivery of the short message either by a deliveryreport or a failure report with a specific mechanism for later delivery.

FIG. 7 is a signaling diagram illustrating the main steps involved in SMMO services. SM MO denotes the capability of the GSM/UMTS system totransfer a short message submitted by the MS 27 to one SME 32 via the SC33, and to provide information about the delivery of the short messageeither by a delivery report or a failure report. The message mustinclude the address of the SME to which the SC shall eventually attemptto relay the short message.

FIG. 8 illustrates the layers of the SMS protocol. A layer named ShortMessage Lower Layers (SM-LL) implies, for example, theCP-DATA/CP-ACK/CP-ERROR SMS service provided by the CM layer for SMS andtransported using DTAP between the MS and the MSC. A Short Message RelayLayer (SM-RL) provides a service to a Short Message Transfer Layer(SM-TL) enabling the SM-TL to send Transfer Protocol Data Units (TPDUs)to its peer entity, receive TPDUs from its peer entity, and receivereports about earlier requests for TPDUs to be transferred. Thedifferent messages used by the SM-RL include RP-DATA, RP-ACK, andRP-ERROR.

The SM-TL also provides a service to a Short Message Application Layer(SM-AL). This service enables the SM-AL to transfer short messages toits peer entity, receive short messages from its peer entity, andreceive reports about earlier requests for short messages to betransferred. The PDUs used by this layer include SMS-DELIVER (to sendSMS messages from the SC 33 to the MS 27), SMS SUBMIT (to transport SMSmessages from the MS 27 to the SC 33), and different Report type PDUssuch as SMS DELIVER REPORT.

FIG. 9 is a simplified block diagram illustrating an architecture forproviding SMS over a generic IP access network 41, as specified by 3GPPfor 3GPP Release-7 in 3GPP TS 23.204. This feature is specified on topof the IMS core network.

FIG. 10 is a signaling diagram illustrating the actions taken when an MTSMS message is forwarded to the UE 27 in the existing CS Fallbacksolution. The MSC-S 26 initiates a paging request 42 for SMS over theSGs interface 25 indicating SMS as the cause. At 43, the UE performs theCS Fallback to GSM/WCDMA and sends a page response 44 in the selectedcell. After optional authentication 45, the SMS is delivered at 46 fromthe MSC-S to the UE. At 47, the UE goes back to the LTE access.

FIG. 11 is a signaling diagram illustrating the actions taken when an MOSMS message is triggered from the UE 27 in the existing CS Fallbacksolution. At 43, the UE performs the CS Fallback to GSM/WCDMA andinitiates a CM Service request 51 for SMS. After optional authenticationand indication to the UE regarding the acceptance of the CM Servicerequest at 52, the SMS is delivered at 53 from the UE 27 to the MSC-S26. At 54, the UE goes back to the LTE access.

Similar procedures to those described in FIGS. 10 and 11 apply also forthe CSoLTE-I solution and MT/MO SMS messages. For the MT SMS case, theMSC-S 26 pages the UE 27 using the SGs interface 25 to the MME 13 andthen via the eNodeB in the LTE radio access network 12. Thereafter, theUE contacts the PMSC 21 using the U8 c interface (shown in FIG. 3) andreplies to the paging request. The MT SMS message is then delivered fromthe PMSC to the UE. As part of this process, the SAE/LTE bearer forCSoLTE-I solution signaling must be activated.

For the MO SMS case, the UE 27 contacts the PMSC 21 using the U8 cinterface and performs a CM Service Request. The MO SMS message is thentransported from the UE to the PMSC. As part of this process, theSAE/LTE bearer for CSoLTE-I solution signaling is established/activatedfor a very short time period.

The main problem with the CS Fallback solution is that all other SAE/LTEbearers being used would also be moved to the GSM/WCDMA because the UEis receiving or sending an SMS message.

The main problem with the CSoLTE-I solution is that the needed SAE/LTEbearers would need to be activated whenever the UE is receiving orsending an SMS message of approximately 200 octets or less, even ifmultiple SMS transferred.

The main problem with using SMS over a generic 3GPP IP access is thatthe access is based on an IMS core network, and the usage for CSoLTEsolutions is a deployment scenario in which an IMS core network is notavailable.

The present invention utilizes the SGs interface for both MT and MO SMSservices. The prerequisite is that the SGs interface is used for MMprocedures, that is, the UE becomes attached in the MSC-S. Thus, thepresent invention applies for the CS Fallback and CSoLTE-I solutions. Inaddition, the NAS-signaling support between the UE 27 and an enhancedMME 64 is extended to provide support for both MT and MO SMS service.

FIG. 12 is a simplified block diagram of an exemplary embodiment of anarchitecture 60 for SMS support in the CSoLTE solutions based on anextended interface (SGs+) 63 according to the teachings of the presentinvention. The functions related to the SMS support are connected to amodified MSC-S 61 which also implements the SGs+ interface. It should benoted that the CS domain may include the MSC-S 61 and an MGW 62 or mayalternatively consist of classical MSC/VLR nodes (not shown).

The existing SGs interface 25 supports limited Mobility Managementprocedures. For example, authentication is not supported. In the presentinvention, an extended SGs+ interface 63 and an extended BSSAP+ protocolare extended with support for DTAP-like transmission of upper layerPDUs. The new SGs+ interface 63 still utilizes connectionless SCCPoperation in one embodiment, so every message must identify the UE 27and the transaction to which a message belongs. The UE's IMSI is used toidentify the subscriber, and the PDU header is used to identifydifferent transactions (for example, the Layer 3 message header for theCP-DATA/CP-ACK/CP-ERROR messages). The new BSSAP+ messages can bedescribed as follows:

BSSAP+-DOWNLINK-DATA-TRANSFER (BDDT). The BDDT message is used totransport entire NAS signaling messages in the direction from the MSC-S61 to an enhanced MME 64 over the SGs+ interface 63. For SMS support,this means the BDDT message provides the SM-LL layer over the SGs+interface in the other direction. The PDUs transferred in this message(referred to herein as SMS-PDUs) are the CP-DATA, CP-ACK, and CP-ERRORas defined in 3GPP TS 24.011. The IMSI is used as the UE identifier.

BSSAP+-UPLINK-DATA-TRANSFER (BUDT). The BUDT message is used totransport entire NAS signaling messages in the direction from the MME 64to the MSC-S 61 over the SGs+ interface 63. For SMS support, this meansthe BUDT message provides the SM-LL layer over the SGs+ interface inthis direction. The SMS-PDUs transferred in this message are theCP-DATA, CP-ACK, and CP-ERROR as defined in 3GPP TS 24.011. The IMSI isused as the UE identifier.

In the same way, the present invention extends SAE NAS signaling betweenthe MME 64 and the UE 27 with similar support to transparently transfer“CS NAS signaling” between the MSC-S 61 and the UE. These messages maybe referred to, for example, as the NAS-X-UPLINK (NASXU) andNAS-X-DOWNLINK (NASXD) messages.

The MSC-S 61 supporting the SMS services over the SGs+ interface 63 ismodified to forward the received MT SMS messages over the SGs+ interfaceusing the BDDT message. The BDDT message includes the initial NAS PDUconsisting of (CP-DATA/RP-DATA/TPDU/SMS-DELIVER, “SMS content”). TheMSC-S sends the BDDT message when the UE 27 is registered for CSservices over the SGs+ interface. The BDDT message is sent to the MME 64where the UE is registered. The MSC-S would normally need to performpaging of the UE in the 2 G/3 G RANs and then forward the SMS after theUE has responded to the paging and a signaling connection has beenestablished to the UE. In the SMS over SGs+ case, the paging is moved tothe SAE/LTE and is performed by the MME 64, if needed, once the SGs+paging request message is received from the MSC-S or when the initialBDDT message is received from the MSC-S.

For MO SMS, the modified MSC-S 61 must also be able to handle theconnectionless nature of the SGs+ interface in some embodiments (whileother embodiments use a connection-oriented solution). This means thatthe first (and subsequent) BUDT message is received without a signalingconnection being established as opposed to existing MO SMS transferprocedures.

The enhanced MME 64 supporting the MO and MT SMS services over the SGs+interface is also modified to perform a Network Triggered ServiceRequest once the initial BDDT message is received from the MSC-S 61.This means that if the UE 27 is in LTE-IDLE state, the MME 64 triggerspaging of the UE. Alternatively, if the UE is in LTE-ACTIVE state, thecontents of the received BDDT message are transferred to the UE in aNAS-X-DOWNLINK message on the S1 connection and then on the RRCconnection from the eNodeB. In the same way, all NAS-X-UPLINK messagesreceived from the UE 27 on the S1 connection are forwarded to the MSC-S61 in BUDT messages.

The description below describes different sequences in which the SGs+interface 63 supports SMS. Four different sequences are shown when MTSMS is triggered and depending on whether the UE 27 is in LTE-IDLE or inLTE-ACTIVE state.

FIG. 13A is a signaling diagram illustrating a first embodiment of aprocedure for MT SMS transfer over SGs+ when the UE 27 is in LTE-IDLEstate. In this embodiment, the MSC-S 61 stores the received SMS messagelocally at 71 and sends a paging request 72 to the MME 64 indicating SMSas the cause. The MME then sends a paging request 73 to the UE via theneeded eNodeBs. The UE responds with a NAS Service Request 74 and a NASsignaling connection is established. Once the NAS signaling connectionis established between the MME and the UE, the MME forwards a pagingresponse (or a service request) 75 to the MSC-S 61 indicating this tothe MSC-S. The MSC-S then forwards the stored SMS message to the MME ina BDDT message 76 over the SGs+ interface 63. The MME forwards the SMSmessage content to the UE 27 in a NAS-X-DOWNLINK message 77 on the S1connection to the eNodeB and then on the RRC connection from the eNodeBto the UE. Thereafter, all communication is transparently tunneledbetween the MSC-S and the UE.

FIG. 13B is a signaling diagram illustrating a second embodiment of aprocedure for MT SMS transfer over SGs+ when the UE 27 is in LTE-IDLEstate. In this embodiment, the MSC-S 61 forwards the received SMSmessage to the MME 64 in a BDDT message 81 over the SGs+ interface 63.The MME then initiates a paging request 82 toward the UE. The UEresponds with a NAS Service Request 83 and a NAS signaling connection isestablished. Once the NAS signaling connection is established betweenthe MME and the UE, the MME forwards the received SMS message to the UEin a NAS-X-DOWNLINK message 84 on the S1 connection to the eNodeB andthen on the RRC connection from the eNodeB to the UE. Thereafter, allcommunication is transparently tunneled between the MSC-S and the UE.

FIG. 14A is a signaling diagram illustrating a first embodiment of aprocedure for MT SMS transfer over SGs+ when the UE 27 is in LTE-ACTIVEstate. In this embodiment, the MSC-C 61 stores the received SMS messagelocally at 91 and sends a paging request message 92 to the MME 64indicating SMS as the cause. At 93, the MME detects that a NAS signalingconnection to the UE already exists. So the MME returns a pagingresponse (or a service request) message 94 to the MSC-S indicating thisto the MSC-S. The MSC-S then forwards the stored SMS message to the MMEin a BDDT message 95 over the SGs+ interface 63. The MME forwards theSMS message content to the UE 27 in a NAS-X-DOWNLINK message 96 on theS1 connection to the eNodeB and then on the RRC connection from theeNodeB to the UE. Thereafter, all communication is transparentlytunneled between the MSC-S and the UE.

FIG. 14B is a signaling diagram illustrating a second embodiment of aprocedure for MT SMS transfer over SGs+ when the UE 27 is in LTE-ACTIVEstate. In this embodiment, the MSC-C 61 forwards the received SMSmessage to the MME 64 in a BDDT message 101 over the SGs+ interface 63.At 102, the MME detects that a NAS signaling connection to the UEalready exists. So the MME forwards the SMS message content to the UE 27in a NAS-X-DOWNLINK message 103 on the S1 connection to the eNodeB andthen on the RRC connection from the eNodeB to the UE. Thereafter, allcommunication is transparently tunneled between the MSC-S and the UE.

The description below describes different sequences in which the SGs+interface 63 supports SMS. One sequence is shown when MO SMS istriggered and when the UE 27 is in LTE-IDLE or in LTE-ACTIVE state.

FIG. 15 is a signaling diagram illustrating an embodiment of a procedurefor MO SMS transfer over SGs+ when the UE 27 is in either LTE-IDLE or inLTE-ACTIVE state. When the UE is in LTE-IDLE state, the procedure beginsby establishing a NAS signaling connection. The UE does this by sendinga NAS Service Request 111 indicating that mobile originated SMS isrequested. The eNodeB in the LTE radio access network 12 forwards therequest to the MME 64. Following authentication at 112, an OK indicationis returned to the UE. The UE then sends a NAS-X-UPLINK message 113 tothe MME with the SMS message content. The MME sends a BUDT message 114to the MSC-S 61 over the SGs+ interface 63 with the SMS message contentfor forwarding to the destination SME through the SMS-GMSC 34.Thereafter, all communication is transparently tunneled between theMSC-S and the UE.

The procedure for MO SMS transfer over SGs+ when the UE 27 is inLTE-ACTIVE state is the same as the procedure for LTE-IDLE state aexcept that the initial steps for establishing a NAS signalingconnection are skipped when the UE is already in LTE-ACTIVE state.

In the embodiments described above, the existing SM-LL layer and relatedprotocol (i.e., messages CP-DATA, CP-ACK, and CP-ERROR) and the existingSM-RL layer and related protocol (i.e., messages RP-DATA, RP-ACK, andRP-ERROR) are kept both in the MSC-S 61 and in the UE 27. In analternative embodiment, these protocols are further optimized bycreating a new single protocol to be used between the MSC-S and the UE.The new single protocol provides the same needed functionality as is nowprovided by these two protocols. As a result, the transaction handlingprovided by the SM-LL layer, for example, may still need to be included.Also, the information included in the RP Destination Address IE may needto be included in the new protocol (this IE contains the address of theSC for the MO SMS case).

In another alternative embodiment, the SGs+ interface 63 may be based onconnection-oriented SCCP rather than the connectionless SCCP describedabove. The main principles of connection-oriented SCCP in the SGs+interface are the same as are also utilized in the A-interface andIu-interface. Thus, when a communication needs to be established, theside initiating the communication initiates the need for an SCCPconnection by sending the SCCP Connection Request message to the remoteside and possibly also including the first higher level message. If theremote node accepts the SCCP Connection request, it returns an SCCPConnection Confirm message to the initiating side. Thereafter, bothsides can use the established SCCP connection.

For the MT-case, sending of a Paging request is not normally used forSCCP connection establishment, but in the SGs+ case, this may optionallybe applied. Thus, the MSC-S initiates the SCCP Connection establishmentwhen the MSC-S sends the BSSAP+-PAGING REQUEST message to the MME. TheMME may then accept the SCCP-level connection when the MME receives theNAS Service Request from the UE. Alternatively, paging may be sent inconnectionless mode, and the SCCP connection is established to the MSC-Sfirst when the MME receives the NAS Service Request from the UE.

In the MO-case, the first message sent from the MME to the MSC-Sinitiates the SCCP connection establishment.

In the connection-oriented SCCP embodiment for MT SMS, the MSC-S 61sends a BSSAP+-PAGING-REQUEST message to the MME 64 with a specialindication that a signaling connection is to be established for the MTSMS once the UE 27 is successfully paged in the LTE radio access network12 and an S1 connection is established to the UE. Thereafter, the MMEestablishes the SCCP signaling connection over the SGs+ interface 63with a new BSSAP+-PAGING-RESPONSE message and the MSC-S uses thecombined signaling connections to deliver the MT SMS message to the UE.In this embodiment, the signaling connection between the MSC-S 61 andthe UE 27 consists of the SGs+ signaling connection to the MME 64, an S1connection to the LTE eNodeB, and an RRC connection to the UE.

A similar approach may be applied for the MO SMS case. When the NASService Request sent from the UE 27 to the MME 64 indicates “MO SMS” asthe establishment cause, the MME establishes the SCCP signalingconnection over the SGs+ interface 63 with a new BSSAP+-SERVICE-REQUESTmessage to the MSC-S 61. If the MSC-S allows the establishment of thatconnection, the UE is notified, and the MO SMS is delivered between theUE and the MSC-S utilizing the SGs+, S1, and RRC signaling connections.It has thus been shown that with the present invention, the changes inthe CS core network are limited to the MSC-S. The rest of the existinginfrastructure for SMS can be used unmodified. This means that allservices related to SMS handling such as Message Waiting are handled inthe Circuit Switched domain of the core network.

When the present invention is utilized in combination with the CSFallback solution, all other SAE/LTE bearers can be kept unmodified andactive in SAE/LTE. As a result, there is no possibility for servicedegradation just because the UE is receiving or sending an SMS message.

When the present invention is used in combination with the CSoLTE-Isolution, there is no need to establish any additional SAE/LTE bearersjust because the UE is receiving or sending an SMS message ofapproximately 200 hundred octets or less even if multiple SMS messagesare transferred.

Finally, the present invention enables SMS to be supported in SAE/LTEwithout the need for deploying an IMS core network, which is aprerequisite for the SMS over a generic 3GPP IP Access network solution.

Although preferred embodiments of the present invention have beenillustrated in the accompanying drawings and described in the foregoingDetailed Description, it is understood that the invention is not limitedto the embodiments disclosed, but is capable of numerous rearrangements,modifications, and substitutions without departing from the scope of theinvention. The specification contemplates all modifications that fallwithin the scope of the invention defined by the following claims.

What is claimed is:
 1. A method of providing a circuit-switched (CS)service to a User Equipment (UE) over an SAE core network and an LTEradio access network, said method comprising the steps of: extending anSGs interface to provide an SGs+ interface between a Mobility ManagementEntity (MME) in the SAE core network and a Mobile Switching CenterServer (MSC-S) wherein the SGs+ interface supports transmission of upperlayer packet data units; transferring CS service messages in SGs+messages sent between the MSC-S and the MME utilizing the SGs+interface, wherein the step of transferring CS service messages includessending from the MSC-S to the MME, an SGs+ downlink data transfermessage including upper layer packet data units destined for aterminating UE, or sending from the MME to the MSC-S, an SGs+ uplinkdata transfer message including upper layer packet data units originatedby an originating UE; and transferring CS service message contentsbetween the MME and the UE via the LTE radio access network in nonaccess stratum (NAS) messages; wherein the CS service message is a ShortMessage Service (SMS) and the step of transferring CS service messagesincludes sending from the MSC-S to the MME, an SGS+ downlink datatransfer message, said SGs+ downlink data transfer message including SMScontrol plane packet data units and SMS message content destined for theterminating UE.
 2. The method according to claim 1, wherein the upperlayer packet data units are transmitted utilizing connection-orientedSignaling Connection Control Part (SCCP) operation.
 3. The methodaccording to claim 1, wherein the upper layer packet data units aretransmitted utilizing connectionless Signaling Connection Control Part(SCCP) operation.
 4. The method according to claim 1, wherein theterminating UE is in LTE-ACTIVE state, and the method further comprisesthe steps of: receiving by the MME, a paging request message from theMSC-S, said paging request message indicating the SGs+ downlink datatransfer message is available for the terminating UE; and returning aresponse message from the MME to the MSC-S without paging theterminating UE; wherein the MSC-S sends to the MME, the SGs+ downlinkdata transfer message in response to receiving the response message. 5.The method according to claim 4, wherein the upper layer packet dataunits are transmitted utilizing connection-oriented Signaling ConnectionControl Part (SCCP) operation.
 6. The method according to claim 4,wherein the upper layer packet data units are transmitted utilizingconnectionless Signaling Connection Control Part (SCCP) operation. 7.The method according to claim 1, wherein the terminating UE is inLTE-ACTIVE state, and the step of transferring CS service messagecontents between the MME and the LTE radio access network includessending a downlink NAS message through the LTE radio access network tothe terminating UE in response to receiving the SGs+ downlink datatransfer message, said downlink NAS message including the upper layerpacket data units.
 8. The method according to claim 1, wherein theterminating UE is in LTEIDLE state, and the method further comprises,prior to receiving the SGs+ downlink data transfer message, the stepsof: receiving by the MME, a paging request message from the MSC-S, saidpaging request message indicating the SGs+ downlink data transfermessage is available; paging the terminating UE by the MME in responseto receiving the SGs+ downlink data transfer message; receiving by theMME, a paging response from the UE requesting mobile terminated SMSservice; and sending a response message to the MSC-S; wherein the MSC-Ssends to the MME, the SGs+ downlink data transfer message in response toreceiving the response message.
 9. The method according to claim 8,wherein the upper layer packet data units are transmitted utilizingconnection-oriented Signaling Connection Control Part (SCCP) operation.10. The method according to claim 8, wherein the upper layer packet dataunits are transmitted utilizing connectionless Signaling ConnectionControl Part (SCCP) operation.
 11. The method according to claim 1,wherein the terminating UE is in LTEIDLE state, and the method furthercomprises the steps of: paging the terminating UE by the MME in responseto receiving the SGs+ downlink data transfer message; and receiving bythe MME, a paging response from the terminating UE requesting mobileterminated SMS service; wherein the step of transferring CS servicemessage contents between the MME and the LTE radio access networkincludes sending a downlink NAS message through the LTE radio accessnetwork to the terminating UE In response to the paging response, saiddownlink NAS message including the upper layer packet data units. 12.The method according to claim 1, wherein the originating UE is inLTE-ACTIVE state, and the step of transferring CS service messagecontents between the MME and the LTE radio access network includesreceiving by the MME, an uplink NAS message through the LTE radio accessnetwork from the originating UE, said uplink NAS message including theupper layer packet data units.
 13. The method according to claim 12,wherein the upper layer packet data units are transmitted utilizingconnection-oriented Signaling Connection Control Part (SCCP) operation.14. The method according to claim 12, wherein the upper layer packetdata units are transmitted utilizing connectionless Signaling ConnectionControl Part (SCCP) operation.
 15. The method according to claim 12,wherein the originating UE is in LTE-IDLE state, and the method furthercomprises, before the MME receives the uplink NAS message, the step of:receiving by the MME, a mobile originated CS service request from theoriginating UE requesting a mobile originated CS service; and sending aresponse indication from the MME to the originating UE establishing aNAS signaling connection; wherein the originating UE sends the uplinkNAS message in response to establishment of the NAS signalingconnection.
 16. The method according to claim 15, wherein the upperlayer packet data units are transmitted utilizing connection-orientedSignaling Connection Control Part (SCCP) operation.
 17. The methodaccording to claim 15, wherein the upper layer packet data units aretransmitted utilizing connectionless Signaling Connection Control Part(SCCP) operation.
 18. The method according to claim 1, wherein the CSservice is the Short Message Service (SMS) and the step of transferringCS service messages includes sending from the MME to the MSC-S, an SGs+uplink data transfer message, said SGs+ uplink data transfer messageIncluding SMS control plane packet data units and SMS message contentoriginated by an originating UE.
 19. An apparatus in a MobilityManagement Entity (MME) in an SAE core network for providing acircuit-switched (CS) service to a User Equipment (UE) through the SAEcore network and an LTE radio access network said apparatus comprising:means for utilizing an extended SGs interface (SGs+) with a MobileSwitching Center Server (MSC-S) in a CS core network to send and receiveSGs+ messages, wherein the SGs+ interface supports transmission of upperlayer packet data units, and said means for utilizing the SGs+ interfaceincludes means for transferring CS service messages in SGs+ messagessent over the SGs+ interface; and means for transferring CS servicemessage contents between the MME and the UE via the LTE radio accessnetwork, wherein the CS service is a Short Message Service, SMS and themeans for transferring CS service messages Includes means for receivingfrom the MSC-S, an SGs+ downlink data transfer message, said SGs+downlink data transfer message including SMS control plane packet dataunits and SMS message content for delivery to a terminating UE.
 20. Theapparatus according to claim 19, wherein the means for utilizing theSGs+ interface includes means for transmitting the upper layer packetdata units utilizing connection-oriented Signaling Connection ControlPart (SCCP) operation.
 21. The apparatus according to claim 19, whereinthe means for utilizing the SGs+ interface includes means fortransmitting the upper layer packet data units utilizing connectionlessSignaling Connection Control Part (SCCP) operation.
 22. The apparatusaccording to claim 19, wherein the means for transferring CS servicemessages also includes means for sending from the MME to the MSC-S, anSGs+ uplink data transfer message, said SGs+ uplink data transfermessage including SMS control plane packet data units and SMS messagecontent originated by an originating UE.
 23. A system for providing acircuit switched (CS) service to a User Equipment (UE) through an SAEcore network and an LTE radio access network, said system comprising: aMobility Management Entity (MME) in the SAE core network; a MobileSwitching Center Server (MSC-S) in a CS core network; and an extendedSGs interface (SGs+) for sending and receiving SGs+ messages between theMME and the MSC-S, wherein the SGs+ interface supports transmission ofupper layer packet data units in CS service messages; wherein the MMEand the MSC-S include means for utilizing the SGs+ interface to transferCS service messages in SGs+ uplink and downlink data transfer messagessent over the SGs+ interface; and wherein the CS service is a ShortMessage Service (SMS) and the means for utilizing the SGs+ interfaceincludes means for sending and receiving SGs+ uplink and downlink datatransfer messages that include SMS control plane packet data units andSMS message content.
 24. The system according to claim 23, wherein theMME also includes means for utilizing a non access stratum (NAS)interface with the LTE radio access network to send and receive extendedNAS messages, said means for utilizing the NAS interface including meansfor transferring CS service message contents between the MME and the LTEradio access network in NAS messages.
 25. The system according to claim23, wherein the means for utilizing the SGs+ interface includes meansfor sending and receiving upper layer packet data units utilizingconnection-oriented Signaling Connection Control Part (SCCP) operation.26. The system according to claim 23, wherein the means for utilizingthe SGs+ interface includes means for sending and receiving upper layerpacket data units utilizing connectionless Signaling Connection ControlPart (SCCP) operation.